Only now White's position becomes losing. This move is part of a flawed plan: White wants to quickly advance his b-pawn, when the right thing to do would be to capture the a6-pawn.
35... d4e4  36. e2d3  36... e4f4 From now on, the game becomes pure calculation. I've always found it curious that some chess players don't like studying endgames, considering them boring. Working on endgames is one of the best ways to improve your calculation since with the limited material, you often can't talk about complex maneuvers but only about mathematics: which pawn will promote first, is it possible to build a fortress, that kind of thing. Studying endgames also brings benefits to the middlegame. 37. b7e7  37... f7e7 